The specs reads 6 seconds from fully open to close, 4 seconds from fully closed to open.
Now the use of a capacitor makes sense. With a capacitor voltage slowly drops to allow the motor to close the valve since any controller immediately removes power to the actuator. Doubtful that the transformer is short on power. The spec reads 12 zone valves/40VA transformer.
Thermostat wiring is a little strange. Is this the unit you're testing with? Is there 4 or 5 wires? W! is heat and that shout be wired to the actuator. ACC+ is 24v to drive accessories and that is strapped to W1 if this is four wire. Anytime a call for heat or cool, voltage is applied to ACC+. The white seems to loop around or are there 2 white wires. Also, two reds? Is the thermostat near the air-handler so it is easy to run a second wire? I know everything works as is ,I'm just trying to learn things here.